CRAL-TRIO domain is a protein

structural domain In molecular biology, a protein domain is a region of a protein's polypeptide chain that is self-stabilizing and that folds independently from the rest. Each domain forms a compact folded three-dimensional structure. Many proteins consist of s ...

that binds small lipophilic molecules. This domain is named after cellular retinaldehyde-binding protein (CRALBP) and TRIO guanine exchange factor. CRALB protein carries 11-cis-

retinol Retinol, also called vitamin A1, is a fat-soluble vitamin in the vitamin A family found in food and used as a dietary supplement. As a supplement it is used to treat and prevent vitamin A deficiency, especially that which results in xerophtha ...

or 11-cis-retinaldehyde. It modulates interaction of retinoids with visual cycle enzymes. TRIO is involved in coordinating

actin remodeling Actin remodeling is the biochemical process that allows for the dynamic alterations of cellular organization. The remodeling of actin filaments occurs in a cyclic pattern on cell surfaces and exists as a fundamental aspect to cellular life. Durin ...

, which is necessary for cell migration and growth. Other members of the family are alpha-

tocopherol Tocopherols (; TCP) are a class of organic chemical compounds (more precisely, various methylated phenols), many of which have vitamin E activity. Because the vitamin activity was first identified in 1936 from a dietary fertility factor in rats, i ...

transfer protein and

phosphatidylinositol Phosphatidylinositol (or Inositol Phospholipid) consists of a family of lipids as illustrated on the right, where red is x, blue is y, and black is z, in the context of independent variation, a class of the phosphatidylglycerides. In such molecul ...

-transfer protein (Sec14). They transport their substrates ( alpha-tocopherol and

phosphatidylcholine Phosphatidylcholines (PC) are a class of phospholipids that incorporate choline as a headgroup. They are a major component of biological membranes and can be easily obtained from a variety of readily available sources, such as egg yolk or soyb ...

, respectively) between different intracellular membranes. Family also include a guanine

nucleotide exchange factor Nucleotide exchange factors (NEFs) are proteins that stimulate the exchange (replacement) of nucleoside diphosphates for nucleoside triphosphates bound to other proteins. Function Many cellular proteins cleave (hydrolyze) nucleoside triphosphates ...

that may function as an effector of RAC1 small

G-protein G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their act ...

. The N-terminal domain of yeast ECM25 protein has been identified as containing a lipid binding CRAL-TRIO domain.

Structure

The Sec14 protein was the first CRAL-TRIO domain for which the structure was determined. The structure contains several

alpha helices The alpha helix (α-helix) is a common motif in the secondary structure of proteins and is a right hand-helix conformation in which every backbone N−H group hydrogen bonds to the backbone C=O group of the amino acid located four residues ear ...

as well as a

beta sheet The beta sheet, (β-sheet) (also β-pleated sheet) is a common motif of the regular protein secondary structure. Beta sheets consist of beta strands (β-strands) connected laterally by at least two or three backbone hydrogen bonds, forming a g ...

composed of 6 strands. Strands 2,3,4 and 5 form a parallel beta sheet with strands 1 and 6 being anti-parallel. The structure also identified a hydrophobic binding pocket for

lipid Lipids are a broad group of naturally-occurring molecules which includes fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include ...

binding.

Human proteins containing this domain

C20orf121; MOSPD2;

PTPN9 Tyrosine-protein phosphatase non-receptor type 9 is an enzyme that in humans is encoded by the ''PTPN9'' gene. Function The protein encoded by this gene is a member of the protein tyrosine phosphatase ( PTP) family. PTPs are known to be signal ...

;

RLBP1 Retinaldehyde-binding protein 1 (RLBP1) also known as cellular retinaldehyde-binding protein (CRALBP) is a 36-kD water-soluble protein that in humans is encoded by the ''RLBP1'' gene. Discovery Cellular retinol binding protein (CRBP) was first d ...

; RLBP1L1; RLBP1L2;

SEC14L1 SEC14-like protein 1 is a protein that in humans is encoded by the ''SEC14L1'' gene. The protein encoded by this gene belongs to the SEC14 cytosolic factor family. It has similarity to yeast SEC14 and to Japanese flying squid RALBP which suggests ...

;

SEC14L2 SEC14L2 is a gene that, in humans, encodes the protein ''SEC14-like protein 2''. Function This gene encodes a cytosolic protein which belongs to a family of lipid-binding proteins including Sec14p, alpha-tocopherol transfer protein, and cellu ...

; SEC14L3; SEC14L4;

TTPA Alpha-tocopherol transfer protein (α-TTP) is a protein that in humans is encoded by the ''TTPA'' gene. See also * Familial isolated vitamin E deficiency Familial isolated vitamin E deficiency or Ataxia with vitamin E deficiency (AVED) is a rar ...

;

References

External links

* - Calculated spatial positions of CRAL-TRIO domains in membrane Peripheral membrane proteins Protein domains Water-soluble transporters {{membrane-protein-stub